Convert CONFIG_SYS_MALLOC_LEN to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MALLOC_LEN

Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/emsdp_defconfig b/configs/emsdp_defconfig
index 9fb35da..1ae7382 100644
--- a/configs/emsdp_defconfig
+++ b/configs/emsdp_defconfig
@@ -4,6 +4,7 @@
 CONFIG_TARGET_EMSDP=y
 CONFIG_SYS_TEXT_BASE=0x00000000
 CONFIG_ENV_SIZE=0x1000
+CONFIG_SYS_MALLOC_LEN=0x10000
 CONFIG_DEFAULT_DEVICE_TREE="emsdp"
 CONFIG_SYS_CLK_FREQ=40000000
 CONFIG_SYS_LOAD_ADDR=0x10000000